The Fluke 887AB AC-DC Differential Voltmeter provides conventional or differential measurements of ac voltages from 1 mV to 1100 V and dc voltages from 0 uV to 1100 V.. When properly working, it can be used as a null meter with essentially infinite Input Impedance from 0 - 11V, and 10 Megohms above that .   Specified accuracy after calibration DC accuracy +- 0.0025% of input + 0.0001% of range +5uV from 0 to 1100 VDC at nominal calibration temperature. AC accuracy +-0.05% of input +0.0025% of range from 1 mV to 500V and frequency up to 5 kHz, with reduced accuracy above 500V and/or at higher frequencies. Conventional (TVM) measurements are made with an accuracy of +/- 3% of the selected range to initially determine the magnitude of the measured voltage.The Differential (NULL) mode is then used with above accuracy  to determine the exact value of the measured voltage,using the front panel 5 readout dials.  Batteries have been removed from this unit and I suspect the charging circuit may be removed also.

This is a good restoration project for a smart retired person who loves older precision instruments!